The parallelized manufacturing of optical microstructures in panels, like e.g. lenses for micro objectives for being used in mobile telephones, is based on the use of glass substrates onto which the optical structures are applied, e.g. by UV replication. FIG. 10a shows a lens reproduced or molded on a glass substrate by UV replication.
For mechanical reasons the substrates may fall below a critical thickness neither during manufacturing nor during operation, wherein the thickness that may be used increases with an increasing substrate diameter and is approximately 400 μm with an 8″ substrate. As one or several substrates are located in the optical path of the optical system, a large thickness of the substrates influences the characteristics of the systems in two ways. On the one hand, the building length of the optics increases and on the other hand large lens thicknesses may lead to optical imaging errors. If, for fulfilling the function, several lenses may be used in the actual direction, several substrates with lens arrays are stacked one onto the other and connected to each other. Air spaces in the axial direction between the lenses here necessitate additional substrates comprising through holes which are to be manufactured with high precision and are to be joined.
FIGS. 10b and 10c show wafer stacks with lens fields and spacer wafers. In FIG. 10c, the spacer wafers are clearly indicated between each individual lens structure, which is why the building length of the optics is increased.
Newer approaches, like the so-called “monolithic lens technology” by a AJI may do without the use of a glass carrier and consist of UV replicable polymer material and may contain the spacer structures for generating air spaces in the axial direction between the lenses. If several lenses are used in the axial direction for fulfilling the optical function, also here several lens wafers are to be stacked on top of each other with high precision (some μm).
FIG. 10d exemplarily shows one of these optics on the basis of the “monolithic lens technology”, as it is among others used by AJI. Problems mainly result when stacking several lens wafers on top of each other with high precision.